Epoxy resin composition, process for producing fiber-reinforced composite materials and fiber-reinforced composite materials

ABSTRACT

An epoxy resin composition comprises (a) an epoxy resin, (b) an anionic polymerization initiator and (c) from 1 to 30 parts by weight per 100 parts by weight of epoxy resin (a) of an aromatic ring-containing proton donor of a polyhydric alcohol and/or a polymercaptan.

FIELD OF THE INVENTION

The present invention relates to an epoxy resin composition that ispreferably used for fiber-reinforced composite materials, and furtherrelates to a process for producing fiber-reinforced composite materialsby impregnating a reinforcing fiber substrate placed in a mold with aliquid thermosetting resin composition, and heating to cure, and furtherrelates to the fiber-reinforced composite materials made thereby.

BACKGROUND OF THE INVENTION

The use of fiber-reinforced composite materials consisting ofreinforcing fibers and matrix resins has been widely extended to thefields including aerospace, sports, and general industry fields, becausefiber-reinforced composite materials make it possible to designmaterials that have benefits of both reinforcing fibers and matrixresins.

As reinforcing fibers, glass fibers, aramid fibers, carbon fibers, boronfibers, and the like may be used. As matrix resins, both thermosettingresins and thermoplastic resins may be used, but thermosetting resinsare more frequently used because reinforcing fibers can be more easilyimpregnated the thermosetting resins. As thermosetting resins, epoxyresins, unsaturated polyester resins, vinyl ester resins, phenolicresins, maleimide resins, cyanate resins, and the like may be used.

For producing fiber-reinforced composite materials, various methods suchas prepreg method, hand lay-up method, filament winding method,pultrusion method, RTM (Resin Transfer Molding) method, and the like maybe used.

Among them, the RTM method where a reinforcing fiber substrate placed ina mold is impregnated with a liquid thermosetting resin, and heated tocure has a great advantage that a fiber reinforced composite materialsof complicated shape can be molded.

Recently, there has been a need for producing fiber-reinforced compositematerials of high fiber volume fraction (Vf) (particularly more thanabout 45%), which are lightweight, and excellent in mechanicalproperties such as strength and elastic modulus, by using the RTMmethod. However, it has been difficult to efficiently producefiber-reinforced composite materials with high Vf in a short time periodusing the conventional RTM method.

In the RTM method, the packing fraction of reinforcing fibers in a moldshould be high to produce fiber-reinforced composite materials with highVf, because the Vf of a product is mainly determined by the packingfraction of reinforcing fibers in a mold. If the packing fraction ishigh, permeability is low, because high packing fraction means low voidfraction. And if the permeability is low, injection time of the resincomposition is lengthened.

If the thermosetting resin composition is heated to cure at a constanttemperature, viscosity of the liquid composition increases, and then,gelation occurs. After gelation, rubbery polymer is obtained. The glasstransition temperature of the polymer increases as the curing reactionprogresses. If the glass transition temperature exceeds the curingtemperature, the polymer turns to a glassy polymer. In general,demolding is carried out after vitrification. For general thermosettingresin compositions, the ratio of the time required from the beginning ofinjection to vitrification to the time from the beginning of theinjection to a point during which the thermosetting resin compositionsmaintain liquid phase with a viscosity adequate for injection is usuallygreater than 6.

In cases of producing fiber-reinforced composite materials whose Vf isnot high, it is possible to carry out the method in a short time(several minutes or about ten minutes), where injection is terminatedbefore the viscosity of the thermosetting resin compositions becomes toohigh, and curing for a predetermined time and demolding are carried outwhile maintaining the mold temperature constant, because injection timeof the resin composition can be short. This method is often called S-RIM(Structural Reactive Injection Molding).

However, in cases fiber-reinforced composite materials with high Vf, itis impossible to carry out the same method mentioned above at the moldtemperature at which the curing reaction is terminated in a short time,because rapid increase of viscosity, and furthermore, gelation occursduring impregnation. On the other hand, if the temperature or thereactivity of the thermosetting resin composition is lowered to preventrapid increase of viscosity during impregnation, the time before thedemolding is increased, and the overall molding process time isincreased. To decrease molding process time, raising the temperature ofthe mold is often used after the termination of injection. This method,however, is not sufficient to decrease total molding process timebecause the method requires additional time to raise and lower thetemperature of the mold.

The object of the present invention is to provide the epoxy resincompositions that have a low ratio of time required from the beginningof the injection to vitrification to time required from the beginning ofthe injection to a point during which the thermosetting resincompositions maintain liquid phase having viscosity adequate forinjection.

Epoxy resin compositions that are similar to those of the presentinvention are disclosed in Japanese patent laid-open publication No.1978-113000. These epoxy resin compositions comprise epoxy resins,imidazole derivatives, methanol and/or ethanol. In these epoxy resincompositions, methanol and/or ethanol function as solvent, and occupy alarge proportion of the compositions. The above patent document alsostates that methanol and (or) ethanol is volatilized before curing. Ifsuch epoxy resin compositions are injected into a mold and heated tocure, it is impossible to volatilize the methanol and/or ethanol. Ifcuring is carried out in the presence of large amounts of methanol and(or) ethanol, cured resin products with crosslinking structure cannot beobtained or cured resin products having very low crosslinking density isobtained. Therefore, these epoxy resin compositions have not been usedas a matrix resin for the RTM method.

Japanese patent laid-open publication No. 1990-103224 discloses epoxyresin compositions comprising epoxy resins, an imidazole derivative,boric acid and mannitol. In the compositions disclosed by the abovepatent, solid bodies prepared by grinding the mixture of imidazolederivatives, boric acid and mannitol is used to blend with the epoxyresins. However, if the reinforcing fiber substrate is impregnated withsuch epoxy resin compositions, heterogeneity of the composition israised because the solid bodies hardly penetrate into bundles ofreinforcing fibers. Thus, curing of the resin compositions isinsufficient in some regions, and cured resin products having high glasstransition temperature cannot be obtained. Therefore, these epoxy resincompositions have not used as a matrix resin for the RTM method.

Journal of Applied Polymer Science, Vol. 30, pp. 531–536 discloses amixture comprising p-cresol glycidyl ether, an imidazole derivative, andisopropyl alcohol. However, if this mixture is reacted, the resultingproduct is a soft linear polymer without a crosslinking structure.Therefore, this mixture cannot satisfy requirements of high glasstransition temperature and strength necessary for a matrix resin in afiber-reinforced composite material.

None of the above compositions or mixtures can increase glass transitiontemperature even when heated to induce reaction, and are not suitablefor advantages such as provided by the present invention which are todecrease the ratio of time from the beginning of the injection tovitrification, to the time from the beginning of the injection to apoint during which the thermosetting resin compositions maintain liquidphase having viscosity adequate for injection.

DETAILED DESCRIPTION OF THE INVENTION

The epoxy resin composition of the present invention solves the statedproblems in the art. The epoxy resin composition of the presentinvention consists of components (a), (b) and (c) defined below, whereinthe amount of component (c) based on 100 parts by weight of thecomponent (a) is 1 to 30 parts by weight, component (a) is liquid, andcomponents (b) and (c) are homogeneously dissolved in component (a).

-   -   (a) epoxy resin    -   (b) anionic polymerization initiator    -   (c) proton donor

A process for producing the fiber-reinforced composite materials of thepresent invention that provides a solution to the afore-stated problems,is described below.

The process for producing fiber-reinforced composite materials where athermosetting resin composition is injected into reinforcing fibersubstrates placed in a mold maintained at the specific temperature T_(m)between 60 to 180° C., and heated to cure at the specific temperatureT_(m) in a manner that the following conditions (7) to (9) aresatisfied:t _(i)≦10  (7)t _(m)≦60  (8)1<t _(m) /t _(i)≦6.0  (9)wherein,

-   -   t_(i): time from the beginning of the injection to the        termination of injection (min.)    -   t_(m): time from the beginning of the injection to the beginning        of the demolding (min.)

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. represents change of cure index versus time obtained bydielectric measurement of the epoxy resin composition of the presentinvention.

FIG. 2. is the illustration of top surface and cross section of the moldused for producing the fiber-reinforced composite materials of thepresent invention.

FIG. 3. is the illustration of top surface and cross section of thearrangement of reinforcing fiber substrate, peel ply and resindistribution medium used in a process for producing planarfiber-reinforced composite materials of the present invention.

FIG. 4. is the illustration of top surface and cross section of thearrangement of reinforcing fiber substrate and core used in a processfor producing sandwich structure fiber-reinforced composite materials ofthe present invention.

Reference number 1 represents a cavity of a mold, reference number 2represents an upper mold, reference number 3 represents lower mold,reference number 4 represents an inlet, reference number 5 represents anoutlet, reference numbers 6 and 7 represent runners, reference numbers 8and 9 represent film-gates, reference numbers 10 and 15 representreinforcing fiber substrates, reference number 11 represents a peel ply,reference number 12 represents a resin distribution medium, referencenumber 13 represents a core, and reference number 14 represents a resinfeeder groove.

BEST MODE FOR CARRYING OUT THE INVENTION

First, the epoxy resin composition of the present invention isdescribed.

The epoxy resin composition of the present invention consists ofcomponents (a), (b) and (c) defined below, wherein the amount of thecomponent (c) based on 100 parts by weight of the component of (a) is 1to 30 parts by weight, the component (a) is liquid, and components (b)and (c) are homogeneously dissolved in component (a).

-   -   (a) epoxy resin    -   (b) anionic polymerization initiator    -   (c) proton donor

The component (a) of the present invention is an epoxy resin. An epoxyresin is defined herein as a compound which has a plurality of epoxygroups in one molecule.

It is preferable that component (a) has one member selected from thegroup consisting of an aromatic ring, a cycloalkane ring, and acycloalkene ring, because the resulting cured resin products have goodheat resistance and good mechanical properties such as elastic modulus.As the cycloalkane ring, a cyclopentane ring, a cyclohexane ring, andthe like, are preferable, and a bicycloalkane ring and a tricycloalkanering, such as norbornane ring and a tricyclo [5.2.1.0^(2.6)] decane ringthat have a cyclopentane ring or a cyclohexane ring in their structures,are also preferable. As the cycloalkene ring, a cyclopentene ring and acyclohexene ring are preferable, and a bicycloalkene ring and atricycloalkene ring that have a cyclopentene ring or a cyclohexene ringin their structures are also preferable.

The viscosity of component (a) of the present invention at 25° C. ispreferably 1 to 30,000 mP s, more preferably 1 to 20,000 mP s, andfurther preferably 1 to 10,000 mP s. If the viscosity is higher thanthese ranges, the initial viscosity of the epoxy resin composition atthe injection temperature of 60 to 180° C. may become high, so that ittakes long to impregnate the reinforcing fibers with the resincomposition. When the component (a) comprises plural epoxy resins, theviscosity of the mixture is used.

Examples of component (a) are aromatic glycidyl ether obtainable fromphenol having plural hydroxyl groups, aliphatic glycidyl etherobtainable from alcohol having plural hydroxyl groups, glycidyl amineobtainable from amine, glycidyl ester obtainable from carboxylic acidhaving plural carboxyl groups, polyepoxide obtainable by oxidizingcompounds having plural double bonds in the molecule, and the like.

Examples of aromatic glycidyl ether are diglycidyl ether obtainable frombisphenol, such that, diglycidyl ether of bisphenol A, diglycidyl etherof bisphenol F, diglycidyl ether of bisphenol AD, diglycidyl ether ofbisphenol S, and diglycidyl ether of tetrabromo bisphenol A, and thelike; polyglycidyl ether of novolac obtainable from phenol, alkylphenol, halogenated phenol, and the like; diglycidyl ether ofresorcinol, diglycidyl ether of hydroquinone, diglycidyl ether of4,4′-dihydroxy-3,3′,5,5′-tetramethylbiphenyl, diglycidyl ether of1,6-dihydroxynaphthalene, diglycidyl ether of9,9′-bis(4-hydroxyphenyl)fluorene, triglycidyl ether oftris(p-hydroxyphenyl)methane, tetraglycidyl ether oftetrakis(p-hydroxyphenyl)ethane, diglycidyl ether having oxazolidonebackbone obtainable by reacting diglycidyl ether of bisphenol A withdi-functional isocyanate, and the like.

Examples of aliphatic glycidyl ether are diglycidyl ether of ethyleneglycol, diglycidyl ether of propylene glycol, diglycidyl ether of1,4-butanediol, diglycidyl ether of 1,6-hexanediol, diglycidyl ether ofneopentyl glycol, diglycidyl ether of cyclohexane dimethanol, diglycidylether of glycerin, triglycidyl ether of glycerin, diglycidyl ether oftrimethylolethane, triglycidyl ether of trimethylolethane, diglycidylether of trimethylolpropane, triglycidyl ether of trimethylolpropane,tetraglycidyl ether of pentaerythritol, diglycidyl ether of dodecahydrobisphenol A, diglycidyl ether of dodecahydro bisphenol F, and the like.

Examples of glycidyl amine are diglycidylaniline,tetraglycidyldiaminodiphenylmethane,N,N,N′,N′-tetraglycidyl-m-xylylenediamine, and 1,3-bis(diglycidylaminomethyl)cyclohexane; triglycidyl-m-aminophenol andtriglycidyl-p-aminophenol having both structures of glycidyl ether andglycidyl amine, and the like.

Examples of glycidyl ester are diglycidyl ester of phthalic acid,diglycidyl ester of terephthalic acid, diglycidyl ester ofhexahydrophthalic acid, diglycidyl ester of dimer acid, and the like.

In addition to the above, triglycidylisocyanurate may be used and epoxyresins having an epoxycyclohexane ring and epoxylated soybean oil, whichare obtainable by oxidizing a compound having plural double bonds in themolecule, and the like, may also be used.

Among them, diglycidyl ether of bisphenol A, diglycidyl ether ofbisphenol F, and diglycidyl ether of bisphenol AD are preferably usedbecause the viscosity of the resin composition thereof, heat resistance,and mechanical properties such as elastic modulus of resulting curedresin products are good.

Component (b) of the present invention is an anionic polymerizationinitiator used as a curing agent of epoxy resins. An anionicpolymerization initiator is defined herein as a compound capable ofinitiating anionic polymerization of the epoxy resin.

The amount of the component (b) is preferably 0.1 to 10 parts by weight,more preferably 0.1 to 5 parts by weight based on 100 parts by weight ofthe component (a). If the amount is greater than these ranges, theexcess component (b) functions as a plasticizer so that the heatresistance and the mechanical properties such as elastic modulus of theresulting cured resin product tend to be poor.

Examples of the component (b) are hydroxides, such as sodium hydroxide,potassium hydroxide, and quaternary ammonium hydroxide; alkoxides, suchas sodium alkoxide; iodides, such as sodium iodide, potassium iodide,quaternary ammonium iodide; tertiary amine, and the like.

Among them, tertiary amine is preferably used as component (b) becauseof its high ability as an anionic polymerization initiator.

Examples of the tertiary amine are triethylamine, dimethylbenzylamine,2,4,6-tris(dimethylaminomethyl)phenol, 1,5-diazabicyclo[4.3.0]nona-5-en,1,8-[5.4.0]undeca-7-en, pyridine, 4-dimethylaminopyridine,3-dimethylaminopropylamine, 3-diethylaminopropylamine,3-dibutylaminopropylamine, 2-diethylaminoethylamine,1-diethylamino-4-aminopentane, N-(3-aminopropyl)-N-methylpropanediamine,1-(2-aminoetheyl)piperazine, 1,4-bis(2-aminoethyl)piperazine,3-(3-dimethylaminopropyl)propylamine, 1,4-bis(3-aminopropyl)piperazine,4-(2-aminoethyl)morpholine, 4-(3-aminopropryl)morpholine, imidazolederivatives, and the like.

Among them, an imidazole derivative is preferably used as component (b)because it has high ability as an anionic polymerization initiator, andit can cure the epoxy resin composition in a short time.

Examples of imidazole derivative are imidazole, 2-methylimidazole,2-ethylimidazole, 2-undecylimidazole, 2-heptadecylimidazole,2-phenylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole,2-phenyl-4-methylimidazole, 1-benzyl-2-phenylimidazole,1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole,1-aminoethyl-2-methylimidazole, and the like.

Among them, imidazoles represented by the following formula I arepreferably used as component (b) because they have extremely highability as an anionic polymerization initiator and they can cure theepoxy resin composition in a short time.

-   -   wherein, R¹ represents a member selected from the group        consisting of hydrogen atom, a methyl group, an ethyl group, a        benzyl group, or a cyanoethyl group; R², R³, and R⁴ each        represent any member selected from the group consisting of a        hydrogen atom, a methyl group and an ethyl group.

The component (c) of the present invention is a proton donor. A protondonor is defined herein as a compound having active hydrogen which canbe donated as a proton to basic compounds.

Also, said active hydrogen of the present invention is defined herein ashydrogen that can be donated to basic compounds as a proton.

The proton donor functions as a chain transfer agent if the resultinganionic species after a proton donation have moderate nucleophilicity.If suitable chain transfer reaction occurs at the beginning of apolymerization, it inhibits the epoxy resin from becoming a too highmolecular weight polymer or inhibits gelation which prevents increase ofviscosity. As a result, it is possible to secure long injection time. Inaddition, the presence of a proton donor enhances anionicpolymerization. By using these two advantageous properties, it ispossible to design a thermosetting resin composition that preventsincrease of viscosity at the beginning of a reaction and acceleratescompletion of a curing reaction.

Based on the above, preferred examples for component (c) are protondonors selected from the group consisting of an alcohol, a phenol, amercaptan, a carboxylic acid and a 1,3-dicarbonyl compound. Thecomponent (c) may be a compound that belongs to multiple categories ofthese exemplary compounds, such as a compound having an alcoholichydroxyl group and a phenolic hydroxyl group.

The component of (a) may include compounds that have a hydroxyl group inthe molecule, in such a case, they are not included in the component of(c).

The amount of the component (c) is 1 to 30 parts by weight andpreferably 1 to 20 parts by weight based on 100 parts by weight of thecomponent (a). If the amount is less than these ranges, it may bedifficult to decrease curing time while preventing increase ofviscosity. If the amount is greater than these ranges, heat resistanceand mechanical properties such as elastic modulus tend to be poor.

The component (c) is introduced to the crosslinking structure byreacting with the epoxy resins, and influences heat resistance andmechanical properties of the cured resin product. Thus, it is preferablethat the component (c) is a compound having two or more active hydrogenin one molecule. When compounds having one active hydrogen in onemolecule are used, crosslinking density of the resulting cured resinproduct tends to be lowered so that heat resistance and mechanicalproperties such as elastic modulus, may be poor.

The compounds that have an aromatic ring, cycloalkane ring or acycloalkene ring are preferably used as component (c) because the heatresistance and mechanical properties of the resulting cured resinproducts such elastic modulus, are good.

An alcohol is preferably used as the component (c) because the resultinganion species after a proton donation has the most preferablenucleophilicity.

An alcohol having a boiling point at atmospheric pressure of more than100° C., preferably more than 140° C., and further preferably more than180° C. at atmospheric pressure, is preferable. If the boiling point islow, voids may occur in the fiber-reinforced composite materials due toevaporation of the component (c) during injection or curing. When two ormore components (c) are used, all such components should satisfy theabove conditions.

An alcohol of which the hydroxyl equivalent weight is more than 100g/mol, preferably more than 120 g/mol, and further preferably 140 g/mol,is preferable. If the equivalent weight is less than these ranges, thepolarity of the alcohol tends to be too high. Thus, its compatibilitywith epoxy resins tends to be insufficient, and difficulty in handlingmay occur. When two or more alcohols are used, a harmonic average ofhydroxyl equivalent weights that is weighted by weight fractions of thealcohols, is used as the hydroxyl equivalent weight of the mixture.

Examples of preferred alcohols are: 1,2-ethanediol (Bp=197, He=31),1,2-propanediol (Bp=187, He=38), 1,3-propanediol (Bp=215, He=38),1,3-butanediol (Bp=208, He=45), 1,4-butanediol (Bp=228, He=45),1,5-pentanediol (Bp=239, He=52), 1,1-dimethyl-1,3-propanediol (Bp=203,He=52), 2,2-dimethyl-1,3-propanediol (Bp=211, He=52),2-methyl-2,4-pentanediol (Bp=198, He=59), 1,4-cyclohexanediol (Bp=150[2.66 kPa], He=58), 1,4-cyclohexanedimethanol (Bp=162 [1.33 kPa]),diethyleneglycol (Bp=244, He=53), triethyleneglycol (Bp=287, He=75),dodecahydro bisphenol A (Bp: no data, He=120), ethylene oxide adduct ofbisphenol A represented by the following formula II (Bp: no data,He=158), propylene oxide adduct of bisphenol A represented by thefollowing formula IV (Bp: no data, He=172), ethylene oxide adduct ofdodecahydro bisphenol A represented by the following formula IV (Bp: nodata, He=164), propylene oxide adduct of dodecahydro bisphenol Arepresented by the following formula V (Bp: no data, He=178), glycerin(Bp=290, He=31), trimethylolethane (Bp=165 to 171 [0.864 kPa], He=40),trimethylolpropane (Bp=292, He=45), and the like, wherein, Bp meansboiling point (° C.), and He means hydroxyl equivalent (g/mol). Examplesof alcohols that comprise four hydroxyl groups in one molecule arepentaerythritol (Bp: no data, He=34), and the like.

Examples of phenols having one active hydrogen in one molecule arephenol, cresol, ethylphenol, n-propylphenol, isopropylphenol,n-butylphenol, sec-butylphenol, tert-butylphenol, cyclohexylphenol,dimethylphenol, methyl-tert-butylphenol, di-tert-butylphenol,chlorophenol, bromophenol, nitrophenol, methoxyphenol, methylsalicylate, and the like. Examples of phenols having two active hydrogenin one molecule are hydroquinone, resorcinol, catechol,methylhydroquinone, tert-butylhydroquinone, benzylhydroquinone,phenylhydroquinone, dimethylhydroquinone, methyl-tert-butylhydroquinone,di-tert-butylhydroquinone, trimethylhydroquinone, methoxyhydroquinone,methylresorcinol, tert-butylresorcinol, benzylresorcinol,phenylresorcinol, dimethylresorcinol, methyl-tert-butylresorcinol,di-tert-butylresorcinol, trimethylresorcinol, methoxyresorcinol,methylcatechol, tert-butylcatechol, benzylcatechol, phenylcatechol,dimethylcatechol, methyl-tert-butylcatechol, di-tert-butylcatechol,trimethylcatechol, methoxycatechol, biphenols such as biphenol,4,4′-dihydroxy-3,3′,5,5′-tetramethylbiphenyl,4,4′-dihydroxy-3,3′,5,5′-tetra-tert-butylbiphenyl, and the like,bisphenols such as bisphenol A, 4,4′-dihydroxy-3,3′,5,5′-tetramethylbisphenol A, 4,4′-dihydroxy-3,3′,5,5′-tetra-tert-butyl bisphenol A,bisphenol F, 4,4′-dihydroxy-3,3′,5,5′-tetramethyl bisphenol F,4,4′-dihydroxy-3,3′,5,5′-tetra-tert-butyl bisphenol F, bisphenol AD,4,4′-dihydroxy-3,3′,5,5′-tetramethyl bisphenol AD,4,4′-dihydroxy-3,3′,5,5′-tetra-tert-butyl bisphenol AD, and compoundsrepresented by the following formulas VI to XII, terpenephenol,compounds represented by the following formulas XIII to XIV, and thelike. Examples of phenols having three active hydrogen in one moleculeare trihydroxybenzene, tris(p-hydroxyphenyl)methane, and the like.Examples of phenols having four active hydrogen in one molecule aretetrakis(p-hydroxyphenyl)ethane, and the like. In addition to the above,other examples may include novolac of phenols such as phenol,alkylphenol, and halogenated phenol.

Examples of mercaptans having one active hydrogen in one molecule aremethanethiol, ethanethiol, 1-propanethiol, 2-propanethiol,1-butanethiol, 2-methyl-1-propanethiol, 2-butanethiol,2-methyl-2-propanethiol, 1-pentanethiol, 1-hexanethiol, 1-heptanethiol,1-octanethiol, cyclopentanethiol, cyclohexanethiol, benzylmercaptan,benzenethiol, toluenethiol, chlorobenzenethiol, bromobenzenethiol,nitrobenzenethiol, methoxybenzenethiol, and the like. Examples ofmercaptans having two active hydrogen in one molecule are1,2-ethanedithiol, 1,3-propanedithiol, 1,4-butanedithiol,1,5-pentanedithiol, 2,2′-oxydiethanethiol, 1,6-hexanedithiol,1,2-cyclohexanedithiol, 1,3-cyclohexanedithiol, 1,4-cyclohexanedithiol,1,2-benzenedithiol, 1,3-benzenedithiol, 1,4-benzenedithiol, and thelike.

Examples of carboxylic acids having one active hydrogen in one moleculeare formic acid, acetic acid, propionic acid, butyric acid, valericacid, caproic acid, caprylic acid, lauric acid, myristic acid, palmiticacid, stearic acid, oleic acid, linoleic acid, linolenic acid,cyclohexanecarboxylic acid, phenylacetic acid, phenoxyacetic acid,benzoic acid, toluic acid, chlorobenzoic acid, bromobenzoic acid,nitrobenzoic acid, methoxybenzoic acid, and the like. Examples ofcarboxylic acids having two active hydrogen in one molecule are malonicacid, methylmalonic acid, phenylmalonic acid, succinic acid, fumaricacid, maleic acid, glutaric acid, diglycolic acid, thioglycolic acid,adipic acid, pimelic acid, cyclohexane-1,2-dicarboxylic acid,cyclohexane-1,3-dicarboxylic acid, cyclohexane-1,4-dicarboxylic acid,phthalic acid, isophthalic acid, terephthalic acid, and the like.

Examples of 1,3-dicarbonyl compounds are 2,4-pentanedione,3-methyl-2,4-pentanedione, 3-ethyl-2,4-pentanedione, 3,5-heptanedione,4,6-nonanedione, 2,6-dimethyl-3,5-heptanedione,2,2,6,6-tetramethyl-3,5-heptanedione, 1-phenyl-1,3-butanedione,1,3-diphenyl-1,3-propanedione, 1,3-cyclopentanedione,2-methyl-1,3-cyclopentanedione, 2-ethyl-1,3-cyclopentanedione,1,3-cyclohexanedione, 2-methyl-1,3-cyclohexanedione,2-ethyl-cyclohexanedione, 1,3-indandione, ethyl acetoacetate, diethylmalonate, and the like.

In the epoxy resin compositions of the present invention, the component(a) should be liquid at least at the injection temperature, and thecomponents (b) and (c) should be uniformly dissolved in component (a).It is not preferable that some part of these components is solid, ormakes separated phase even if all of these are liquid, because partialheterogeneity of compositions may occur during impregnation. However,even if it is impossible for these components to make homogeneoussolution at room temperature, they can be used if they can satisfy theabove conditions through heating.

In addition to the above components, the epoxy resin compositions of thepresent invention may comprise a surfactant, an internal release agent,a pigment, a flame retardant, antioxidant, UV absorbent, and the like.

It is most preferable that these additives are homogeneously dissolvedin the epoxy resin composition. Although these additives are nothomogeneously dissolved in the epoxy resin composition, there are noproblems if they maintain a stable colloid in the form of a droplet or aparticle. In this case, the diameter of the droplet or the particle ispreferably less than 1 μm and more preferably less than 0.3 μm. Ifdiameter of the droplet or the particle is larger than these ranges, itmay be difficult for the droplet or particle to pass gaps in thereinforcing fibers, so that heterogeneity of compositions may occur.

The initial viscosity of the epoxy resin compositions of the presentinvention at 25° C. is preferably 1 to 30,000 mPa s, more preferably 1to 20,000 mPa s and further preferably 1 to 10,000 mPa s. If theviscosity is higher than these ranges, the initial viscosity of theepoxy resin compositions at the injection temperature of 60 to 180° C.may become high, so that it takes long time to impregnate thereinforcing fibers with the resin composition.

The epoxy resin composition of which initial increase of the viscosityis low, and which have lengthened injection time and shortened curingtime are preferable for the present invention.

When curing reaction is fast, it is difficult to monitor the change ofthe viscosity by conventional methods. Monitoring the change of ionicviscosity by means of dielectric measurement is, however, possible eventhough the curing reaction is fast. The ionic viscosity may be used formonitoring a progress of curing reaction as well as initial viscositychange because it can be measured after gelation, increases along with aprogress of curing and is saturated along with completion of curing. Anormalized logarithmic value of which the minimum has been set to 0% andmaximum (saturation) has been set for 100% is called the cure index.This index is used to describe a curing profile of a thermosettingresin. By using the time required for the cure index to reach 10% as astandard for initial increase of viscosity, and time required for thecure index to reach 90% as a standard for curing time, suitableconditions wherein initial increase of viscosity is low and curing timeis short, may be conveniently described. It is preferable that the epoxyresin composition of the present invention satisfies the followingconditions (1) to (3) at a specific temperature T between 60 to 180° C.It is more preferable that the epoxy resin composition of the presentinvention satisfies the following conditions (1) to (3′) at a specifictemperature between 60 to 180° C.1≦t ₁₀≦10  (1)3≦t ₉₀≦30  (2)1<t ₉₀ /t ₁₀≦3  (3)1<t ₉₀ /t ₁₀≦2.5  (3′)wherein,

-   -   t₁₀: time required for the cure index to reach 10% from the        beginning of the measurement, which is measured by dielectric        measurement at the temperature T (min.)    -   t₉₀: time required for the cure index to reach 90% from the        beginning of the measurement at the temperature T, which is        measured by dielectric measurement (min.)

As curing proceeds, the glass transition temperature of the resincomposition rises. In general, demolding is carried out after the glasstransition temperature of the resin composition exceeds the curingtemperature. Thus, the time required for the glass transitiontemperature of the cured resin product to reach curing temperature maybe used as a standard for curing time. It is preferable that the epoxyresin composition of the present invention satisfies the followingconditions (4) to (6). It is more preferable that the epoxy resincomposition of the present invention satisfies the following conditions(4) to (6′).1≦t ₁₀≦10  (4)3≦t _(v)≦30  (5)1<t _(v) /t ₁₀≦3.0  (6)1<t _(v) /t ₁₀≦2.5  (6′)wherein,

-   -   t₁₀: time required for the curing index to reach 10% from the        beginning of the measurement, which is measured by dielectric        measurement at the temperature T(min.)    -   t_(v): time required for the glass transition temperature of the        cured resin product to reach the temperature T from the        beginning of the measurement, that is vitrification time, which        is measured at the temperature T (min.)

The epoxy resin composition of the present invention have thecharacteristic of which the initial increase of viscosity is low, thatis, injectable time is long, and curing time is short. Therefore, it issuitable for the RTM method where the mold temperature is maintainedconstant from injection to demolding.

The epoxy resin composition of the present invention is also suitablefor the RTM method where the mold temperature is raised aftertermination of the injection to cure the resin composition. And theepoxy resin composition of the present invention has the advantage ofshorten the molding time, too.

The epoxy resin composition of the present invention is applicable toall methods where a liquid thermosetting resins is used, such as handlay-up method, pultrusion method, filament winding method, and the like,as well as RTM method. And the epoxy resin composition of the presentinvention has the advantage to shorten the molding time in all thesemethods.

A process for producing fiber-reinforced composite materials isdescribed below.

In accordance with the present invention, it is possible to producefiber-reinforced composite materials with high Vf with goodproductivity.

In the RTM method of the present invention, it is necessary that themold temperature be maintained at the specific temperature T_(m) that isbetween 60 to 180° C., and the following conditions (7) to (9) andpreferably (7) to (9′) be satisfied.ti≦10  (7)t _(m)≦60  (8)1<t _(m) /t _(i)≦6.0  (9)1<t _(m) /t _(i)≦5.0  (9′)wherein,

-   -   t_(i): time from the beginning of injection to the termination        of injection (min.)    -   t_(m): time from the beginning of injection to the beginning of        demolding (min.)

In the RTM method of the present invention, the mold temperature ismaintained at the specific temperature T_(m) between 60 to 180° C. toomit raising and lowering of the mold temperature and, as a result, toshorten molding time. However, some variation of the mold temperaturedepending on time and place is somewhat allowed. Specifically,difference ΔT between T_(m) and the temperature measured at any point ofa surface of a cavity during a period from the beginning of injection tothe beginning of demolding should be −20 to 20° C., preferably −10 to10° C., and more preferably −5 to 5° C. If there are any portion whereΔT is too large, viscosity of the resin composition increases to giverise to gelation and to prevent impregnation. If there are any portionwhere ΔT is too small, partial failure of curing occurs, which is notpreferable.

Time t_(i) used herein means time from the beginning of injection to thetermination of injection. Here, the beginning of injection means a pointwhen the resin composition starts to pour into the mold, and thetermination of injection means a point when the resin composition isstopped to supply into the mold. When the mold has plural inlets ofwhich time of injection at each inlets are different from one another,or termination time of injection at each inlets are different from oneanother, t_(i) is set for time from the last beginning of injection tothe last termination of injection.

Time t_(m) used herein means time from the beginning of injection to thebeginning of demolding. When the mold has plural inlets of whichbeginning time of injection at each inlets are different from oneanother, t_(m) is set for time from the last beginning of injection tothe beginning of the demolding.

Epoxy resin compositions, unsaturated polyester resin compositions,vinyl ester resin compositions, phenolic resin compositions, maleimideresin compositions, and cyanate ester resin compositions are preferablyused in the RIM method of the present invention.

-   -   In the RTM method of the present invention, it is difficult to        measure the viscosity at the temperature T_(m) directly because        the viscosity of the resin composition varies rapidly. However,        it is possible to estimate the initial viscosity at the        temperature T_(m) by measuring the viscosity at low temperature,        which is easy to measure, and calculating by the formula WLF        represented as formula A.        In(η/η₀)=−[A(T−T ₀)]/[B+(T−T ₀)]  [Formula A]    -    wherein, In represents natural logarithm, T represents absolute        temperature (K), T₀ represents reference temperature (K), η        represents viscosity of a resin composition at T (mPa s), η₀        represents viscosity of a resin composition at T₀ (mPa s), and A        and B represent constants that are inherent to a liquid.

Specifically, four to six temperatures at which viscosity is easy tomeasure are selected, and one of them is set for T₀. Then, viscosity ateach temperature is measured. Constants A and B are calculated by linearregression analysis using formula A. Finally, initial viscosity at T_(m)is determined by using these parameters.

In the RTM method of the present invention, if initial viscosity of theresin composition at T_(m) is low, impregnation of reinforcing fiberswith the resin compositions is good. Therefore, initial viscosity atT_(m) measured by the WLF formula is preferably 0.1 to 300 mPa s, morepreferably 0.1 to 200 mPa s, and further preferably 0.1 to 100 mPa s.

In the RTM method of the present invention, glass transition temperatureof fiber-reinforced composite materials after t_(m) from the beginningof injection is preferably greater than T_(m)−15° C. and more preferablygreater than T_(m). If the glass transition temperature is less thanthese ranges, matrix resin is likely to flow or creep at T_(m), andfiber-reinforced composite materials may be deformed by force exertedwhen demolding is carried out.

In the RTM method of the present invention, Vf of fiber-reinforcedcomposite materials is preferably 40 to 85% and more preferably 45 to85% to obtain fiber-reinforced composite materials that are light-weightand excellent in their mechanical properties, such as strength andelastic modulus. If Vf is less than these ranges, mechanical propertiesof the fiber-reinforced composite materials, such as strength andelastic modulus, may be insufficient. If Vf is greater than theseranges, it may be necessary to inject the resin compositions into a moldin which reinforcing fibers are placed in a very high density. Thus, itmay be difficult to inject the resin composition into the mold.

In the RTM method of the present invention, a plastic film, a metal orplastic plate, connection parts such as a bolt, a nut, a U link, a hingeand the like, and core materials such as a foam core, a honeycomb-core,and the like, in addition to the reinforcing fibers, may be placed inthe mold.

In the RTM method of the present invention, reinforcing fiber substratessuch as strands, fabrics, mats, knits, and braids are placed in the moldprior to injection of the resin compositions. Reinforcing fibersubstrates may be cut and laminated to the desired shape and placed inthe mold with other materials such as core materials, if necessary.Also, preforms of the reinforcing fiber substrates formed to the desiredshape by methods, such as stitching or press with heat after applying asmall amount of tackifier may be placed in the mold. A combination ofreinforcing fiber substrates and other materials such as core materialsmay be used for the preforms.

In the RTM method of the present invention, a closed mold having acavity enclosed by only stiff materials or an open mold having a cavityenclosed by stiff materials and bagging film may be used.

In the RTM method of the present invention, metals, such as carbonsteel, steel alloy, cast iron, aluminum, aluminum alloy, nickel alloy,FRP (Fiber Reinforced Plastic) or wood may be used for the materials ofthe mold. Among them, metals are preferable because their thermalconductivity is good.

Examples of bagging film to be used for the open mold are polyamide,polyimide, polyester, silicone, and the like.

In the RTM method of the present invention, the closed mold ispreferably used because the closed mold makes it possible to inject aresin composition by pressing and facilitates removal of heat producedby curing of the resin compositions.

The mold may be provided with the function to heat by circulation of aheat medium or a conventional heater.

In the RTM method of the present invention, the mold has inlets toinject a resin composition and outlets to flow out a resin composition.There are no limitation to the number or places of the inlets andoutlets.

It is preferable to introduce a resin composition into a cavity througha fan gate or a film gate, specially when planar fiber-reinforcedcomposite materials are molded.

In the RTM method of the present invention, it is preferable to applyrelease agents to the surface of the mold to demold the resultingfiber-reinforced composite materials easily. Examples of release agentsinclude the silicone type, fluorine type, plant oil type, wax type, PVAtype, and the like.

In the RTM method of the present invention, a gel coat or a gel coatsheet such as disclosed in Japanese patent laid-open publication No.1993-318468 and Japanese patent laid-open publication No. 2001-288230may be used to provide the properties to surface such as color, gloss,hardness, water resistance, weatherability, and the like.

In the RTM method of the present invention, the shorter is the injectiontime, the shorter is the molding time. In cases when planarfiber-reinforced composite materials are molded, it is preferable torapidly distribute the resin composition in a planar form in the mold,and then, impregnate it mainly in the direction of thickness of thereinforcing fiber substrates to decrease the injection time. For this, aresin distribution medium, a mold having a resin distribution grooves atthe surface of a cavity, and a core having a resin distribution groovesare preferably used.

As disclosed in U.S. Pat. No. 4,902,215, a resin distribution mediummeans a planar structure through which resin compositions are easilyflowed. Metallic nets are preferably used because their heat resistanceis high, and they do not dissolve in matrix resins. Plastic nets whichhardly dissolve or swell even if they contact with matrix resins, suchas polyethylene, polypropylene, nylon, polyester, and the like are alsopreferably used.

When a mold has a resin distribution grooves at the surface of a cavity,it is preferable that the cross section of the grooves is in a shapethat does not inhibit demolding such as a rectangle, trapezoid, triangleor semicircle. Arrangement of the grooves depends on the shape of thecavity. In general, although there are no limitations to the arrangementof the grooves, parallel lines or a lattice is preferably used. For amold having a planar cavity, the grooves must be placed at least at onesurface of the cavity to introduce a resin composition from an inlet tothe grooves. Opposing surface may or may not have grooves.

When a foam core or balsa core is used, the resin distribution groovesmay be placed at the core. It is preferable that the grooves are placedon the entire surface where the core contacts with the reinforcing fibersubstrates. Arrangement of the grooves depends on the shape of thecavity and the core. Although there are no limitations to thearrangement of the grooves, parallel lines or a lattice is preferablyused. When a core having the grooves is used, it is necessary to designa mold in which an injected resin composition is introduced to groovesat the beginning. As disclosed in U.S. Pat. No. 5,958,325, a core havingresin main feeder grooves and microgrooves may be used.

In the RTM method of the present invention, a pre-mixed single resincomposition in a single tank may be transferred and injected into amold. Alternatively, a plurality of liquids in separate tanks may betransferred to a mixer where the transferred liquids are mixed togetherto form resin composition, which is then injected into a mold.

In the RTM method of the present invention, the injection pressure(pressure when resin compositions are injected into a mold) ispreferably 0.1 to 1.0 MPa and more preferably 0.1 to 0.6 MPa. Ifinjection pressure is too low, injection time may become too long. Ifinjection pressure is too high, it may not be economical becauseexpensive plumbing, molds, and presses are required. Various pumps orpressing of a tank is used to transfer liquids.

In the RTM method of the present invention, it is preferable to usesuction from outlets by a vacuum pump and the like when the resincomposition is injected into a mold. Suction is effective to shorten theinjection time and to prevent occurrence of dry areas or voids in thefiber-reinforced composite materials.

In the RTM method of the present invention, post-cure may be performedin a heater such as an oven after demolding to increase heat resistanceof the fiber-reinforced composite materials. It is preferable that thepost-cure is performed at 100 to 200° C. for 10 to 480 minutes.

The fiber-reinforced composite materials of the present invention aredescribed below.

For the fiber-reinforced composite materials of the present invention,glass fibers, aramid fibers, carbon fibers and boron fibers arepreferably used as reinforcing fibers. Among them, carbon fibers arepreferably used because fiber-reinforced composite materials oflightweight and good mechanical properties, such as strength and elasticmodulus, can be obtained.

The reinforcing fibers may be one of chopped fibers, continuous fibersor a combination thereof. Continuous fibers are preferable because theirhandling is easy and it is possible to obtain high Vf fiber-reinforcedcomposite materials by using them.

In the fiber-reinforced composite materials of the present invention,the reinforcing fibers may be used in the form of strands. However,reinforcing fiber substrates that are processed into reinforcing fibersin the form of mats, woven fabrics, knits, braids or unidirectionalsheet are preferably used.

Among them, woven fabrics are preferably used because their handling iseasy, and fiber-reinforced composite materials having high Vf can beeasily obtained.

A ratio of real volume of the reinforcing fibers to apparent volume ofthe fabrics is set for packing fraction of the fabrics. The packingfraction is determined by the formula W/(1000 t ρ_(f)), wherein Wrepresents areal weight (g/m²), t represents thickness (mm), and ρ_(f)represents density of the reinforcing fibers (g/cm³). The areal weightand thickness of the fabrics can be determined according to JIS R 7602.It is easy to produce fiber-reinforced composite materials with high Vffrom fabrics with high packing fraction. Thus, the packing fraction ofthe fabrics is preferable 0.10 to 0.85, more preferably 0.40 to 0.85,and further preferably 0.50 to 0.85.

Vf of the fiber-reinforced composite materials is preferably 40 to 85%,and more preferably 45 to 85% to obtain fiber-reinforced compositematerials which have high specific strength and specific elasticmodulus.

The specific strength of the fiber-reinforced composite materials of thepresent invention is preferably greater than 250 MPa cm³/g, morepreferably greater than 300 MPa cm³/g, and further preferably greaterthan 350 MPa cm³/g if lightweight and high strength fiber-reinforcedcomposite materials are required. The specific strength (MPa cm³/g) canbe calculated from the following formula B using tensile strength σ(MPa) determined according to ASTM D 3039 and density of thefiber-reinforced composite materials ρ_(c) (g/cm³) determined accordingto ASTM D 792.specific strength=σ/ρ_(c)  [Formula B]

In general, fiber-reinforced composite materials are anisotropic.Therefore, tests are made in a direction where maximum strength isobtained.

The specific elastic modulus of the fiber-reinforced composite materialsof the present invention is preferably greater than 28 GPa cm³/g. morepreferably greater than 32 GPa cm³/g, and further preferably greaterthan 34 GPa cm³/g if lightweight and high elastic modulusfiber-reinforced composite materials are required. The specific elasticmodulus (GPa cm³/g) can be calculated from the following formula C usingtensile modulus E (GPa) determined according to ASTM D 3039 and densityof the fiber-reinforced composite materials ρ_(c) (g/cm³) determinedaccording to ASTM D 792.specific elastic modulus=E/ρ _(c)  [Formula C]

In general, fiber-reinforced composite materials are anisotropic.Therefore, tests are made in a direction where maximum elastic modulusis obtained.

The preferred form of the fiber-reinforced composite materials is amonolithic plate. Another preferred form of the fiber-reinforcedcomposite materials is a sandwich structure in which thefiber-reinforced composite materials are positioned on both surfaces ofthe core.

Still another preferred form of the fiber-reinforced composite materialsis a canape structure in which single planar fiber-reinforced compositematerials are positioned on one surface of the core.

Examples of a core of sandwich structure and canape structure are ahoneycomb-core made of aluminum or aramid, a foam core made ofpolyurethane, polystyrene, polyamide, polyimide, polyvinyl chloride,phenolic resin, acrylic resin, epoxy resin, and the like, wood includingbalsa, and the like. Among these, the foam core is preferably usedbecause it can produce lightweight fiber-reinforced composite materials.

The density of the core is preferably 0.02 to 0.10 g/cm³ and morepreferably 0.02 to 0.08 g/cm³ to obtain lightweight fiber-reinforcedcomposite materials. The density of the core can be determined accordingto ISO 845.

If the glass transition temperature of the core is low, it is likelythat the core deforms during molding. Therefore, the glass transitiontemperature of the core is preferably more than 80° C., more preferablymore than 100° C. and further preferably more than 120° C.

In the sandwich structure fiber-reinforced composite materials, thehigher is the shear modulus of elasticity of the core, the higher is theflexural stiffness. Therefore, the shear modulus of elasticity ispreferably more than 2.0 MPa, more preferably more than 4.0 MPa, andfurther preferably more than 6.0 Mpa. The shear modulus of elasticity ofthe core is determined according to ASTM C 273.

If the independent bubble content of the core is great, it is difficultfor the resin composition to penetrate into the core. Therefore, theindependent bubble content of the core is preferably more than 0.70,more preferably more than 0.80, and further preferably more than 0.90.The independent bubble content of the core is determined according toASTM D 1940.

When the fiber-reinforced composite materials of the present inventionare used for the stylish surface such as the outer skin of automobiles,the surface roughness R_(a) of at least one side of the fiber-reinforcedcomposite materials is preferably less than 1.0 μm, more preferably lessthan 0.6 μm, and further preferably less than 0.4 μm. The surfaceroughness R_(a) is determined according to ISO 468.

The fiber-reinforced composite materials of the present invention areparticularly suitable for structural parts, outer skins and aerodynamicparts of transports such as spacecrafts including rockets, artificialsatellites, and the like, aircrafts, trains, marines, automobiles,motorcycles, bicycles, and the like, because they are lightweight andhave good mechanical properties such as strength and elastic modulus.

Because the productivity of the fiber-reinforced composite materials ofthe present invention is high, they are preferably used for structuralparts, outer skins and aerodynamic parts of motorcycles and automobilesof mass production. Specific examples are structural parts such asplatforms, outer skins of automobiles such as front apron, hood, roof,hard top (a removable roof of a convertible car), a piller, trunk lid,door, fender and side mirror cover, and the like, and aerodynamic partssuch as front air dam, rear spoiler, side air dam, engine under cover,and the like.

The fiber-reinforced composite materials of the present invention can beused for other applications besides the above applications. Specificexamples are interior trim materials of automobiles such as aninstrument panel.

EXAMPLES

The following examples will explain the present invention morespecifically. Each property was determined by the following methods.Also, the following resin components were used in the examples.

Component a

-   -   “Epo Tohto” YD128: registered trademark, produced by Tohto Kasei        Co., Ltd., epoxy resin (diglycidylether of bisphenol A)        Component b    -   2-methylimidazole: produced by Shikoku Kasei Kogyo Co., Ltd.,        imidazole derivative        Component c    -   glycerin: produced by Tokyo Kasei Kogyo Co., Ltd., alcohol    -   1,2-ethanediol: produced by Tokyo Kasei Kogyo Co., Ltd., alcohol    -   benzyl alcohol: produced by Wako Junyaku Kogyo, Ltd., alcohol    -   isopropyl alcohol: produced by Tokyo Kasei Kogyo Co., Ltd.,        alcohol    -   propylene glycol: produced by Wako Junyaku Kogyo, Ltd., alcohol    -   “Rikaresin” PO-20: registered trademark, produced by Shin Nippon        Rika Co., Ltd., alcohol (propylene oxide adduct of bisphenol A)    -    2,4-dimethylphenol: produced by Tokyo Kasei Kogyo Co., Ltd.,        phenol    -    propionic acid: produced by Tokyo Kasei Kogyo Co., Ltd.,        carboxylic acid        Measurement of Viscosity of a Resin Composition

Viscosity of the component (a) and that of the resin composition justafter the composition was prepared, were measured according to ISO2884-1 by using the cone-and-plate rotary viscometer. The viscometer wasTVE-30H manufactured by Toki Sangyo Co., Ltd. The rotor used was 1°34′×R24. An amount of each sample was 1 cm³.

Method for Estimating Viscosity at the Temperature T_(m) by Using theFormula WLF

Viscosity of the resin composition was measured at 10, 30, 50 and 70° C.according to the above method. The reference temperature T₀ was set for10° C. The constants A and B were calculated by linear regressionanalysis by using formula A. Then, viscosity at T_(m) was estimated fromthese parameters.In(η/η₀)=−[A(T−T ₀)]/[B+(T−T ₀)]  [Formula A]wherein, In represents natural logarithm, T represents absolutetemperature (K), T₀ represents reference temperature (K), η representsviscosity of the resin composition at T (mPa s), η₀ represents viscosityof the resin composition at T₀ (mPa s), and A and B represent constantsthat are inherent to a liquid.Dielectric Measurement

Curing of the resin composition was monitored by dielectric measurement.The dielectric measurement device was MDE-10 curing monitor manufacturedby Holometrix-Micromet. The TMS-1 inch sensor was installed in the lowerplate of the programmable mini-press MP2000. The O-ring made of Viton,which had internal diameter of 31.7 mm and thickness of 3.3 mm, wasplaced on the lower plate of the press, and the temperature of the presswas set for predetermined T. The epoxy resin composition was poured intothe inside of the O-ring, and the press was closed. Change of ionicviscosity of the resin composition vs. time was monitored. Thedielectric measurement was carried out at the frequencies of 1, 10, 100,1,000 and 10,000 Hz.

The cure index was calculated by the following formula D. Then, a ratiot₉₀/t₁₀ (wherein, t₁₀: time required for the cure index to reach 10%,t₉₀: time required for the cure index to reach 90%) was determined.cure index=[log(α)−log(α_(min))]/[log(α_(max))−log(α_(min))]×100  [Formula D]wherein,

-   -   log: common logarithm    -   unit of cure index: %    -   α: ionic viscosity (Ωcm)    -   α_(min): minimum ionic viscosity (Ωcm)    -   α_(max): maximum ionic viscosity (Ωcm)        Measurement of Glass Transition Temperature of a Cured Resin        Product

The O-ring made of Viton, which had internal diameter of 31.7 mm andthickness of 3.3 mm, was installed at the lower plate of theprogrammable mini-press MP2000, and the temperature of the press was setfor predetermined T. And then, the resin composition was added to theinterior of the O-ring, and the press was closed. The resin compositionwas cured for the predetermined period. The resulting cured resinproduct was cut to make a sample having a width of 12 mm and length of40 mm. The sample was measured by the viscoelastometer ARES manufacturedby Rheometric Scientific with a rectangular torsion mode, and withtemperature raising rate of 20° C./min, and frequency of 1 Hz, todetermine a peak of Loss modulus G″. If the number of the peaks is two,a peak of lower temperature is selected. From the peak of Loss modulusG″, the glass transition temperature was determined.

Estimation of t_(v)

Glass transition temperatures of the cured resin after 6, 8, 10, 12, 14and 20 minutes at the predetermined temperature T were measuredaccording to the above method. The time necessary for the glasstransition temperature of the cured resin products to reach T (t_(v))was estimated by interpolation of these data.

Preparation of a Cured Resin Plate

Stainless steel spacers with a dimension of 150 mm×150 mm×2 mm wereinstalled at the lower plate of a press, and the temperature of thepress was set for the predetermined temperature T. And then, the resincomposition was added to the interior of the spacer, and the press wasclosed. After 20 minutes, the press was opened to obtain the cured resinplate.

Measurement of Flexural Modulus of a Cured Resin

A sample with width of 10 mm and length of 60 mm was made by cutting theabove cured resin plate. Flexural modulus was measured with the 3 pointsflexural test according to ISO 178. The test device used was theTensilon 4201 manufactured by Instron Company. The crosshead speed usedwas 2.5 mm/min, span space was 32 mm, and the temperature duringmeasurement was 23° C.

Measurement of Tensile Elongation of a Cured Resin

Tensile elongation was measured by using the above cured resin plateaccording to ISO 527-2. The test device used was the Tensilon 4201manufactured by Instron Company. The temperature during measurement was23° C.

Measurement of Fiber Volume Fraction (Vf) of a Fiber-reinforcedComposite Material

The fiber volume fraction (Vf) of a fiber-reinforced composite materialwas measured according to ASTM D 3171.

Measurement of Density (ρ_(c)) of a Fiber-reinforced Composite Material

Density ρ_(c) of a fiber-reinforced composite material was measuredaccording to ASTM D 792.

Measurement of Glass Transition Temperature of a Fiber-reinforcedComposite Material

The inlet side of the fiber-reinforced composite material was cut tomake a sample with width of 12 mm and length of 55 mm. The sample wasmeasured by the viscoelastometer ARES manufactured by RheometricScientific with a rectangular torsion mode and with a temperatureraising rate of 20° C./min and frequency of 1 Hz, to determine the peakof Loss modulus G″. If there are two peaks detected, the peak of lowertemperature is selected. From the peak of Loss modulus G″, glasstransition temperature was determined.

Measurement of Specific Strength and Specific Elastic Modulus of aFiber-reinforced Composite Material by Tensile Test

The fiber-reinforced composite material was cut to make a sample withwidth of 12.7 mm and length of 229 mm, which had length directionidentical to the 0° direction. The 0° tensile strength σ (MPa) and 0°tensile modulus E (GPa) were measured with the sample according to ASTMD 3039. The test device used was the Tensilon 4208 manufactured byInstron Company. The crosshead speed was 1.27 mm/min, and thetemperature during measurement was 23° C. Specific strength (MPa cm³/g)and specific elastic modulus (GPa cm³/g) were determined by thefollowing formulas B and C and ρ_(c) measured in the above.specific strength=σ/ρ_(c)  [Formula B]specific elastic modulus=E/ρ _(c)  [Formula C]Measurement of Density of a Core

Density of cores was measured according to ISO 845.

Measurement of Glass Transition Temperature of a Core

Glass transition temperature of core was measured using a sample withwidth of 12 mm and length of 55 mm according to SACMA SRM18R-94. Thetest device used was the viscoelastmeter ARES manufactured by RheometricScientific. The measurement was made with a rectangular torsion mode,and with temperature raising rate of 5° C./min, and frequency of 1 Hz,to determine storage modulus G′. From the onset of the storage modulusG′, glass transition temperature was determined.

Measurement of Shear Modulus of Elasticity of a Core

Shear modulus of elasticity of a core was measured using a sample withwidth of 50 mm, length of 150 mm and thickness of 10 mm according toASTM C 273.

Measurement of Surface Roughness R_(a) of a Fiber-reinforced CompositeMaterial

Surface roughness R_(a) of a fiber-reinforced composite material wasmeasured according to ISO 845. The test device used was Surftest 301manufactured by Mitutoyo.

Examples 1, 2, 3 and 5

The component (b) represented in Table 1, below, was added to thecomponent (c). This mixture was heated to 90° C. to make a solution. Theresulting solution was maintained at 70° C. The component (a) that hadbeen heated to 70° C. was added to the solution. The solution wasstirred for 1 minute to give an epoxy resin composition. The epoxy resincomposition of example 1 was turbid to white at 70° C. but became auniform solution at 100° C. The epoxy resin compositions of examples 2,3 and 5 were uniform solutions at 70° C.

The t₉₀/t₁₀ of the epoxy resin compositions of examples 1, 2, 3 and 5were 1.7, 1.8, 1.9 and 2.3, respectively, which were all satisfactoryvalues (FIG. 1 shows change of cure index of the resin compositions ofexamples 1 and 2 vs. time by dielectric measurement).

The t_(v)/t₁₀ of the epoxy resin compositions of examples 1, 2, 3 and 5were 1.9, 2.3, 2.5 and 1.9, respectively, which were all satisfactoryvalues.

The flexural modulus the cured resin products of examples 1, 2, 3 and 5were 3.5 GPa, 3.2 GPa, 3.1 GPa, and 3.4 GPa, respectively. The tensileelongation of the cured resin products of examples 1, 2, 3 and 5 were4.1%, 4.7%, 4.8% and 4.5% respectively. These values were sufficientlyhigh.

Example 4

The component (b) represented in Table 1 was added to the component (c).This mixture was heated to 90° C. to make a solution. The resultingsolution was maintained at 70° C. The component (a) which had beenheated to 70° C. was added to the solution. The solution was stirred for1 minute to give an epoxy resin composition. The epoxy resin compositionwas a uniform solution at 70° C.

The t₉₀/t₁₀ was 2.2, which was a satisfactory value.

The t_(v)/t₁₀ was 2.9, which was a relatively satisfactory value.

The flexural modulus of the cured resin product was 3.0 GPa, which was arelatively high value. The tensile elongation of the cured resin productwas 4.4%, which was a sufficiently high value.

Examples 6 and 7

The component (b) represented in Table 1 was added to the component (c).This mixture was heated to 90° C. to make a solution. The resultingsolution was maintained at 70° C. The component (a) which had beenheated to 70° C. was added to the solution. The solution was stirred for1 minute to give an epoxy resin composition. The epoxy resincompositions of examples 6 and 7 were uniform solutions at 70° C.

The t₉₀/t₁₀ of the epoxy resin compositions of examples 6 and 7 were all2.1, which were satisfactory values. The t_(v)/t₁₀ of the epoxy resincompositions of examples 6 and 7 were 2.4 and 2.5, respectively, whichwere satisfactory values.

The flexural modulus of the cured resin products of examples 6 and 7were 3.2 GPa and 3.1 GPa, respectively. The tensile elongation of thecured resin products of examples 6 and 7 were 4.3% and 4.0%. Thesevalues were sufficiently high.

Comparative Example 1

The component (b) represented in Table 1 was grinded with an agatemortar to give fine particulates. This was added to the component (a)that had been heated to 70° C. The mixture was stirred and dispersed for1 minute to give an epoxy resin composition. The epoxy resin compositionbecame a uniform solution at 100° C.

The t₁₀ of the epoxy resin composition was equal to those of examples 1and 2. The t₉₀/t₁₀, however, was 3.6, which was not a satisfactory value(FIG. 1 shows change of cure index of the resin composition vs. time bydielectric measurement).

The t_(v)/t₁₀ was 3.9, which was not a satisfactory value.

The flexural modulus of the cured resin product was 3.1 GPa, which wassufficiently high value, but the tensile elongation of the cured resinproduct was 1.7%, which was not a satisfactory value.

Comparative Example 2

The component (c) that had been heated to 70° C. was added to thecomponent (a) represented in Table 1. This was stirred for 1 minute togive an epoxy resin composition. Dielectric measurement showed thatthere was little change in the ion viscosity. The epoxy resincomposition of comparative example 2 was still liquid when observed byopening a programmable mini-press after 30 minutes.

Comparative Example 3

The component (b) represented in Table 1 was added to the component (c).This mixture was heated to 90° C. to make a solution. The resultingsolution was maintained at 70° C. The component (a) that had been heatedto 70° C. was added to the solution. The solution was stirred for 1minute to give an epoxy resin composition. The epoxy resin compositionwas turbid to white, even at 100° C.

In the dielectric measurement, the α_(max) could not be measured becauseion viscosity changed too slowly.

Also, t_(v) could not be estimated because the glass transitiontemperature of the epoxy resin composition was only 52° C. after 20minutes.

Example 8

A monolithic plate of fiber-reinforced composite material was preparedby using the epoxy resin composition of example 5 at the moldtemperature of 90° C.

The initial viscosity of the epoxy resin composition of example 5 at 90°C., which was estimated by the formula WLF, was 36 mPa s.

Referring to FIG. 2, the mold used comprised a rectangularparallelepiped cavity with a width of 600 mm, length 600 mm and height1.5 mm (reference number 1), upper mold (reference number 2), and lowermold (reference number 3), wherein the upper mold had an inlet(reference number 4) and outlet (reference number 5), the lower mold hadrunners (reference numbers 6 and 7) and film gates (reference numbers 8and 9) corresponding to the inlet and the outlet.

For reinforcing fiber substrates, a 600 mm×600 mm square carbon fiberfabrics C06343 (using T300B-3K, areal weight 192 g/m², Toray Co., Ltd.),which had sides parallel to weft and warp of the carbon fiber fabrics,was used. For a peel ply, a 600 mm×600 mm square polyester fabric wasused. For resin distribution medium, 580 mm×580 mm square nylon net wasused.

Referring to FIG. 3, after six reinforcing fiber substrates (referencenumber 10), a peel ply (reference number 11) and a resin distributionmedium (reference number 12) were placed in the cavity of the mold, andthe mold was closed. The pressure of the inside of the mold that wasmaintained at 98° C. decreased to atmospheric pressure −0.1 MPa with avacuum pump connected to the outlet. The epoxy resin composition ofexample 5 was injected into the mold with an injection pressure of 0.2MPa. The injection was terminated after 6.5 minutes from the beginningof injection. The mold was opened after 25 minutes from the beginning ofinjection, and a fiber-reinforced composite material was obtained.

The Vf of the fiber-reinforced composite material was 52%.

The glass transition temperature of the fiber-reinforced compositematerial was 98° C.

The specific strength and specific elastic modulus of thefiber-reinforced composite material were 400 MPa cm³/g and 40 GPa cm³/g,which were sufficiently high values.

The surface roughness R_(a) of the fiber-reinforced composite materialwas 0.38 μm, which was a satisfactory value.

Example 9

A monolithic plate of fiber-reinforced composite material was preparedby using the epoxy resin composition of example 5 at the moldtemperature of 105° C. The initial viscosity of the epoxy resincomposition of example 5 at 105° C., which was estimated by the formulaWLF, was 20 mPa s.

The mold used, reinforcing fiber substrates, a peel ply and a resindistribution medium were all the same as those of example 8. Referringto FIG. 3, after six reinforcing fiber substrates (reference number 10),a peel ply (reference number 11) and a resin distribution medium(reference number 12) were placed in the cavity of the mold, and themold was closed. The pressure of the inside of the mold that wasmaintained at 105° C. was decreased to atmospheric pressure −0.1 MPawith a vacuum pump connected to the outlet. The epoxy resin compositionof example 5 was injected into the mold with an injection pressure of0.2 MPa. The injection was terminated after 3.3 minutes from thebeginning of injection. The mold was opened after 12.0 minutes from thebeginning of injection, and a fiber-reinforced composite material wasobtained.

The Vf of the fiber-reinforced composite material was 52%.

The glass transition temperature of the fiber-reinforced compositematerial was 116° C.

The specific strength and specific elastic modulus of thefiber-reinforced composite material were 380 MPa cm³/g and 40 GPa cm³/g,which were sufficiently high values.

The surface roughness R_(a) of the fiber-reinforced composite materialwas 0.44 μm, which was a satisfactory value.

Example 10

A monolithic plate fiber-reinforced composite material was prepared byusing the epoxy resin composition of comparative example 1 at the moldtemperature of 105° C.

The mold used, reinforcing fiber substrates, a peel ply and a resindistribution medium were the same as those of example 8. Referring toFIG. 3, after six reinforcing fiber substrates (reference number 10), apeel ply (reference number 11) and a resin distribution medium(reference number 12) were placed in the cavity of the mold, and themold was closed. The pressure of the inside of the mold that wasmaintained at 105° C. decreased to atmospheric pressure −0.1 MPa with avacuum pump connected to the outlet. The epoxy resin composition ofcomparative example 1 was injected into the mold with an injectionpressure of 0.2 MPa. The injection was terminated after 2.8 minutes fromthe beginning of injection. The mold was opened after 12.0 minutes fromthe beginning of injection, and a fiber-reinforced composite materialwas obtained.

The glass transition temperature of the fiber-reinforced compositematerial was 88° C., which was very much lower than the moldtemperature.

Example 11

A fiber-reinforced composite material of sandwich structure was preparedby using the epoxy resin composition of example 5 at the moldtemperature of 90° C.

Referring to FIG. 2, the mold used comprised a rectangularparallelepiped cavity with a width of 600 mm, length 600 mm and height13.5 mm (reference number 1), upper mold (reference, number 2), andlower mold (reference number 3), wherein the upper mold had an inlet(reference number 4) and outlet (reference number 5), the lower mold hadrunners (reference numbers 6 and 7) and film gates (reference numbers 8and 9) corresponding to the inlet and the outlet.

For the reinforcing fiber substrates, rectangular (width 600 mm, length598 mm) carbon fiber fabrics C06343 (using T300B-3K, areal weight 192g/m², Toray Co., Ltd.) of which sides are parallel to weft and warp ofthe carbon fiber fabrics were used.

For the core, Rohacell 511G which had a thickness of 12.7 manufacturedby Rohm Company was used, which was cut to width of 600 mm and length of598 mm, and on which resin distribution grooves with a cross section ofrectangle with width of 1 mm and depth of 2 mm are engravedlongitudinally parallel to one another with intervals of 25 mm on theupper and the lower surfaces. The density, the glass transitiontemperature, and the shear modulus of the Rohacell 511G were 0.052g/cm³, 152° C., and 19 MPa.

Referring to FIG. 4, after two reinforcing fiber substrates (referencenumber 15), a core (reference number 13) having resin distributiongrooves (reference number 14) and two reinforcing fiber substrates(reference number 15) were overlapped over one another in the cavity ofthe mold, and the mold was closed. The reinforcing fiber substrates andthe core were placed in a manner such that gaps of 1 mm width wereformed beside the inlet and the outlet, and nylon nets were set to thegaps to introduce the resin composition into the resin distributiongrooves at the lower surface of the core. Then, the pressure of theinside of the mold that was maintained at 90° C. was decreased toatmospheric pressure −0.1 MPa with a vacuum pump connected to theoutlet. The epoxy resin composition of example 5 was injected into themold with an injection pressure of 0.2 MPa. The injection was terminatedafter 4.8 minutes from the beginning of injection. The mold was openedafter 20.0 minutes from the beginning of injection, and afiber-reinforced composite material was obtained.

The surface roughness R_(a) of the fiber-reinforced composite materialwas 0.39 μm, which was satisfactory value.

Example 12

A sandwich structure fiber-reinforced composite material was prepared byusing the epoxy resin composition of example 5 at the mold temperatureof 105° C.

The mold used, reinforcing fiber substrates and a core were the same asthose of example 11.

Referring to FIG. 4, after two reinforcing fiber substrates (referencenumber 15), a core (reference number 13) having resin distributiongrooves (reference number 14) and two reinforcing fiber substrates(reference number 15) were overlapped over one another in the cavity ofthe mold, and the mold was closed. The reinforcing fiber substrates andthe core were placed in a manner such that gaps of 1 mm width wereformed beside the inlet and the outlet of the cavity, and nylon netswere set to the gaps to introduce the resin composition into the resindistribution grooves at the lower surface of the core. The pressure ofthe inside of the mold that was maintained at 105° C. was decreased toatmospheric pressure −0.1 MPa with a vacuum pump connected to theoutlet. The epoxy resin composition of example 5 was injected into themold with an injection pressure of 0.2 MPa. The injection was terminatedafter 2.2 minutes from the beginning of injection. The mold was openedafter 10.0 minutes from the beginning of injection, and afiber-reinforced composite material was obtained.

The surface roughness R_(a) of the fiber-reinforced composite materialwas 0.45 μm, which was a satisfactory value.

INDUSTRIAL APPLICABILITY

According to the present invention, a high Vf fiber-reinforced compositematerial will be made by the RTM method with good productivity.

-   -   The epoxy resin composition of the present invention has the        characteristic of long injectable time and short curing time.        Therefore, a high Vf fiber-reinforced composite material will be        produced with good productivity by using the epoxy resin        composition of the present invention.

Because the fiber-reinforced composite materials produced by the processof the present invention or the fiber-reinforced composite materialsobtained from the epoxy resin composition of the present invention havegood mechanical properties such as strength and elastic modulus, theyare preferably used for structural parts, outer skins and aerodymamicparts of transports, such as spacecrafts including rockets, artificialsatellites, and the like, aircrafts, trains, marines, automobiles,motorcycles, bicycles, and the like. Among them, they are particularlypreferably used for structural parts, outer skins and aerodymamic partsof motorcycles and automobiles produced in mass quantities.

TABLE 1 Comparative Examples examples 1 2 3 4 5 6 7 1 2 3 composition ofepoxy component a “Epo-Tohto” YD128 100 100 100 100 100 100 100 100 100100 resin (% by weight) (di-functional aromatic epoxy resin) component b2-methylimidazole 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 — 3.0 (imidazolederivative) component c glycerin (alcohol) 3.1 — — — — — — — 3.1 4.01,2-ethandiol (alcohol) — 2.1 — — — — — — — — benzyl alcohol — — 3.6 — —— — — — — (alcohol) isopropyl alcohol — — — 2.1 — — — — — — (alcohol)propylene glycol — — — — 2.0 — — — — — (alcohol) “Rikaresin” PO-20 — — —— 6.0 — — — — — (alcohol) 2,4-dimethylphenol — — — — — 4.1 — — — —(phenol) propionic acid — — — — — — 2.5 — — — (carboxylic acid)viscosity of the component (a) at 25° C. (Pa s) 12.0 12.0 12.0 12.0 12.012.0 12.0 12.0 12.0 12.0 initial viscosity of the epoxy resincomposition at 25° C. (Pa s) 12.3 11.9 6.3 6.9 8.7 8.7 10.6 13.4 12.827.8 curing properties of the temperature T (° C.) 100 100 100 100 100100 100 100 100 100 epoxy resin composition t₁₀ (min.) 3.5 3.3 3.2 3.83.8 3.1 4.2 3.2 — — t₉₀ (min.) 6.0 6.1 6.2 8.2 8.9 6.4 8.8 11.5 — —t₉₀/t₁₀ 1.7 1.8 1.9 2.2 2.3 2.1 2.1 3.6 — — glass transition temperature94 85 86 — 95 89 — — — — after 6 minutes at T (° C.) glass transitiontemperature 115 105 103 88 111 106 84 68 — — after 8 minutes at T (° C.)glass transition temperature 117 110 109 96 118 113 99 85 — — after 10minutes at T (° C.) glass transition temperature 120 113 112 104 120 115103 98 — — after 12 minutes at T (° C.) glass transition temperature 121115 114 108 122 118 107 106 — — after 14 minutes at T (° C.) glasstransition temperature 124 116 116 112 125 121 113 115 — 52 after 20minutes at T (° C.) t_(v) (min.) 6.6 7.5 8.0 11.0 7.3 7.3 10.5 12.5 — —t_(v)/t₁₀ 1.9 2.3 2.5 2.9 1.9 2.4 2.5 3.9 — — physical properties offlexural modulus of elasticity (GPa) 3.5 3.2 3.1 3.0 3.4 3.2 3.1 3.1 — —the cured resin product tensile elongation (%) 4.1 4.7 4.8 4.4 4.5 4.34.0 1.7 — —

TABLE 2 Examples 8 9 10 molding mold temperature 90 105 105 conditionT_(m)(° C.) t_(i) (min.) 6.5 3.3 2.8 t_(m) (min.) 25.0 12.0 12.0t_(m)/t_(i) 3.8 3.6 4.3 viscosity 10° C. 154500 154500 391000 of the 30°C. 3930 3930 13350 resin 50° C. 439 439 922 composition 70° C. 102 102112 (mPa s) viscosity at T_(m) 36 20 9 estimated by the formula WLFphysical degree of impregnation overall overall overall properties Vf(%) 52 52 — of the Density ρ_(c) (g/cm³) 1.5 1.5 — composite glasstransition temp- 98 116 88 material erature after t_(m) (° C.) specificstrength by 400 380 — tensile test (MPa · cm³/g) specific elastic 40 40— modulus by tensile test (GPa · cm³/g) surface roughness R_(a) 0.380.44 — (μm)

TABLE 3 Examples 11 12 molding mold temperature T_(m) (° C.) 90 105condition t_(i) (min.) 4.8 2.2 t_(m) (min.) 20.0 10.0 t_(m)/t_(i) 4.24.5 viscosity of the 10° C. 154500 154500 resin composi- 30° C. 39303930 tion (mPa s) 50° C. 439 439 70° C. 102 102 viscosity at T_(m)estimated 36 20 by the formula WLF physical Density (g/cm³) 0.052 0.052properties of glass transition temperature 152 152 core member (° C.)shear modulus of elasticity 19 19 (MPa) surface degree of surfaceroughness R_(a) (μm) 0.39 0.45 the composite material

1. An epoxy resin composition, comprising: component (a) epoxy resin,component (b) anionic polymerization initiator and component (c) protondonor, wherein the amount of component (c) based on 100 parts by weightof component (a) is 1 to 30 parts by weight; component (a) is a liquid;and components (b) and (c) are homogeneously dissolved in component (a);component (c) is at least one member selected from the group consistingof a polyhydric alcohol with two hydroxy functional groups and amercaptan with two mercapto functional groups; and component (c) has anaromatic ring.
 2. The epoxy resin composition according to claim 1,wherein said component (b) is a tertiary amine.
 3. The epoxy resincomposition according to claim 2, wherein said component (b) is animidazole derivative.
 4. The epoxy resin composition according to claim3, wherein said component (b) is represented by the following generalformula I:

wherein, R¹ represents a member selected from the group consisting ofhydrogen atom, a methyl group, an ethyl group, a benzyl group and acyanoethyl group; R², R³ and R⁴ independently one on other represent amember selected from the group consisting of hydrogen atom, a methylgroup and an ethyl group.
 5. The epoxy resin composition according toclaim 1, wherein said component (c) is a polyhydric alcohol.
 6. Theepoxy resin composition according to claim 5, wherein said component (c)is a polyhydric alcohol which has a boiling point of greater than 1000°C. at atmospheric pressure.
 7. The epoxy resin composition according toclaim 1, wherein the initial viscosity of the composition at 250° C. isbetween 1 to 30,000 mPa s.
 8. The epoxy resin composition according toclaim 1, wherein the epoxy resin composition satisfies the followingconditions (1) to (3) at a specific temperature T that t₉₀ is between 60to 1800° C.:1≦t ₁₀≦10  (1)3≦t ₉₀≦30  (2)1≦t ₉₀ /t ₁₀≦3  (3) wherein, t₁₀ is time (in minutes) required for thecure index to reach 10% from the beginning of the measurement, which isdetermined by dielectric measurement at the temperature T and t₉₀ istime (in minutes) required for the cure index to reach 90% from thebeginning of the measurement, which is determined by dielectricmeasurement at the temperature T.
 9. The epoxy resin compositionaccording to claim 1, wherein the epoxy resin composition satisfies thefollowing conditions (4) to (6) at a specific temperature T that isbetween 60 to 180° C.:1≦t ₁₀≦10  (4)3≦t _(v)≦30  (5)1t _(v) /t ₁₀3  (6) wherein, t₁₀ is time required for the cure index toreach 10% from the beginning of the measurement, which is determined bydielectric measurement at the temperature T(min.) and t_(v) is time (inminutes) required for the glass transition temperature of the curedresin product to reach T from the beginning of the measurement at thetemperature T.
 10. A cured product of the epoxy resin composition ofclaim 1.